This invention relates to improved formation of three-dimensional objects from a fluid-like medium on a substantially layer-by-layer basis. The invention more particularly relates to the improved formation of three-dimensional objects by stereolithography utilizing techniques to overcome difficulties in quickly forming objects with minimized distortion.
1. Related Art
Rapid Prototyping and Manufacturing (RPandM) is the name given to a field of technologies that can be used to form three-dimensional objects rapidly and automatically from three-dimensional computer data representing the objects. Rapid prototyping and manufacturing can be considered to include three classes of technologies: (1) stereolithography, (2) selective deposition modeling, and (3) laminated object manufacturing.
The stereolithography class of technologies creates three-dimensional objects by successively forming layers of a fluid-like medium adjacent to previously formed layers of medium and selectively solidifying these layers to form and adhere laminae (i.e. solidified layers). These laminae are solidified according to cross-sectional data representing successive slices of the three-dimensional object. Typically, adhesion between successive laminae occurs by chemical bond formation between the two laminae (e.g. inter-lamina cross-linking) during polymerization. In alternative embodiments, it is possible that adhesion could occur by application of a separate adhesive or by other mechanical bonding. In summary, adhesion may occur via an adhesive or cohesive phenomenon.
One specific stereolithography technology is known simply as stereolithography, and it uses a liquid medium that is selectively solidified by exposing it to stimulation. The liquid medium is typically a photopolymerizable material (i.e. resin) and the stimulation is typically visible or ultraviolet electromagnetic radiation. The radiation is typically produced by a laser. Liquid-based stereolithography is disclosed in various patents, applications, and publications, of which a number are briefly described in the Related Patents, Applications and Publications section hereinafter. Another stereolithography technology is known as selective laser sintering (SLS). Selective laser sintering is based on the selective solidification of layers of a powdered medium by exposing the layers to infrared electromagnetic radiation to sinter or fuse the particles. Selective laser sintering is described in U.S. Pat. No. 4,863,538 issued Sep. 5, 1989, to Deckard. A third technology is known as three-dimensional printing (3DP). Three-dimensional printing is based on the selective solidification of layers of a powdered medium which are solidified by the selective deposition of a binder thereon. Three-dimensional printing is described in U.S. Pat. No. 5,204,055 issued Apr. 20, 1993, to Sachs, et al.
The present invention is primarily directed to stereolithography using liquid-based building materials (i.e. medium). It is believed, in addition, that the techniques of the present invention may have application in the other stereolithography technologies for the purposes of reducing distortion and/or speeding object formation.
Selective deposition modeling (SDM) involves the build-up of three-dimensional objects by selectively depositing solidifiable material on a lamina-by-lamina basis according to cross-sectional data representing slices of the three-dimensional object. One such technique is called fused deposition modeling (FDM) and involves the extrusion of streams of heated, flowable material which solidify as they are dispensed onto the previously formed laminae of the object. Fused deposition modeling is described in U.S. Pat. No. 5,121,329 issued Jun. 9, 1992, to Crump. Another technique is called ballistic particle manufacturing (BPM) which uses a 5-axis, ink-jet dispenser to direct particles of a material onto previously solidified layers of the object. Ballistic particle manufacturing is described in PCT Publication Nos. WO 96/12607 published May 2, 1996, by Brown, et al.; WO 96/12608 published May 2, 1996, by Brown et al.; WO 96/12609 published May 2, 1996, by Menhennett et al.; and WO 96/12610 published May 2, 1996, by Menhennett et al. A third technique called multijet modeling (MJM) involves the selective deposition of droplets of material from multiple ink jet orifices to speed the building process. Multijet modeling is described in PCT Publication Nos. WO 97/11835 published Apr. 3, 1997, by Earl et al.; and, WO 97/11837 published Apr. 3, 1997, by Leyden et al. (both assigned to 3D Systems, Inc., as is the instant application).
Laminated object manufacturing (LOM) techniques involve the formation of three-dimensional objects by the stacking, adhering, and selective cutting, in a selected order, of sheets of material, according to the cross-sectional data representing the three-dimensional object to be formed. Laminated object manufacturing is described in U.S. Pat. No. 4,752,352 issued Jun. 21, 1988, to Feygin; and U.S. Pat. No. 5,015,312 issued May 14, 1991, to Kinzie; and in PCT Publication WO 95/18009 published Jul. 6, 1995, by Morita et al.
As noted above, the techniques of the instant invention are directed primarily to liquid-based stereolithography object formation. However, it is believed that the techniques may be applied in the selective deposition modeling technologies to reduce object distortion and/or to decrease object formation time. Some of the selective deposition modeling technologies may use a technique sometimes referred to as xe2x80x9cMinimum Layer Secondsxe2x80x9d. This technique requires that a minimum amount of time lapse from the beginning of building one layer to the beginning of building the next layer, so that there is sufficient time for heat built up in the layer to dissipate. If a layer takes less than the Minimum Layer Seconds to build, the balance of the Minimum Layer Seconds is counted down before beginning the next layer. If a delay occurs, it occurs after the layer is completely built. This technique does not teach or suggest the partial creation of a lamina, then a delay, then the completion of the lamina.
Various techniques for decreasing distortion, and techniques that utilize multiple exposures of an ultraviolet-curable fluid during creation of three-dimensional objects formed using stereolithography, have been described previously, such as, for example: (1) U.S. Pat. No. 5,104,592 issued Apr. 14, 1992, to Hull et al., (2) Japanese Laid Open Patent Application 63-145015A published Jun. 17, 1988, by Itarni et al., (3) U.S. Pat. No. 4,945,032 issued Jul. 31, 1990, to Murphy et al., (4) Appendix A of U.S. Pat. No. 4,575,330 issued Mar. 11, 1986, to Hull, (5) European Patent 0 250 121 B1 issued Nov. 2, 1994, to Pornerantz et al., and (6) U.S. Pat. No. 5,965,079 to Gigi et al. assigned to 3D Systems, Inc.
U.S. Pat. No. 5,104,592 issued Apr. 14, 1992, to Hull et al., discloses various stereolithography techniques for reducing curl distortion. The first curl reduction technique disclosed is the xe2x80x9cdashed linexe2x80x9d technique, in which a stereolithography line that is part of a vertical or horizontal formation is drawn with breaks in the line instead of a solid line. Thus, the pulling force normally transmitted along the vector is reduced, and the curl effect is reduced. The second curl reduction technique is the xe2x80x9cbent-linexe2x80x9d technique, in which a stereolithography line that is part of a vertical or horizontal formation is drawn with bends in the line instead of a straight line. In this way, the pulling force normally transmitted along the vector is reduced, and the curl effect is reduced. The third curl reduction technique is the xe2x80x9csecondary structurexe2x80x9d technique, in which a stereolithography line which is part of a vertical or horizontal formation is drawn so that it does not adhere directly to the line below or beside it, but is attached, after it is formed, with a secondary structure. As such, the pulling force down the vector is eliminated, the bending moment on adjacent lines is reduced, and the curl effect is reduced.
One type of secondary structure is known as xe2x80x9crivetsxe2x80x9d and comprises supporting lines of lower exposure and an area of higher exposure (a xe2x80x9crivetxe2x80x9d) for connecting support lines from adjacent layers together. The fourth curl reduction technique is the xe2x80x9cmulti-passxe2x80x9d technique, in which a stereolithography line which is part of a vertical or horizontal formation is drawn so that it does not adhere directly to the line below or beside it until the material is substantially reacted. In this way, the pulling force down the vector is reduced, the structure is more rigid so it can resist deformation, and the curl effect is reduced. This reference fails to teach a step of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of vectors, let alone teaching the use of a device to count down a desired delay time.
Japanese Laid Open Patent Application 63-145015A published Jun. 17, 1988, by Itami et al. discloses stereolithography techniques to address inadequate hardness resulting from the small degree of radical polymerization during hardening, and which result in the product being deformed under its own weight. The techniques disclosed irradiate the same position on the liquid photopolymerizable resin material several times at specified time intervals using identical raster exposures. First, a layer of liquid is added to a container (i.e. vat). Then the liquid is irradiated with light which is raster scanned in the xe2x80x9cmain scanning directionxe2x80x9d while moving in the xe2x80x9csubscanning directionxe2x80x9d in order to partially harden the liquid. The same positions of the resin are raster scanned again at a specified time interval, by raster scanning in the same xe2x80x9cmain scanning directionxe2x80x9d as for the first pass, while moving in the same xe2x80x9csubscanning directionxe2x80x9d as for the first pass. For each position of the resin, the time interval between the first and second irradiation is the same. The main scanning direction is the direction in which the raster lines cured by the laser beam are situated, and the subscanning direction is the direction in which these raster lines propagate as they are cured next to each other, and is perpendicular to the main scanning direction. The laser beam movement in the main scanning direction is accomplished with the beam reflecting off of a revolving polygon mirror, and the laser beam movement in the subscanning direction is accomplished by either moving the liquid container in the subscanning direction or by reflecting the beam off of a rotating flat mirror. This reference fails to teach curing lines in one direction for a first pass and curing lines in a different direction for a second pass. In addition, this reference fails to teach a step of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of vectors in a different direction than the direction of the first set of vectors, let alone teaching the use of a device to count down a desired delay time.
U.S. Pat. No. 4,945,032 issued Jul. 31, 1990, to Murphy et al. discloses stereolithography techniques that provide increased strength and solvent resistance of the formed object so distortion is minimized. In preferred practice, these techniques are carried out as a series of repeated, rapid scans of the ultraviolet-curable liquid surface by a computer directed laser light source in the production of each surface layer. This reference fails to teach a step of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of vectors, let alone teaching the use of a device to count down a desired delay time.
U.S. Pat. No. 4,575,330 issued Mar. 11, 1986, to Hull discloses general stereolithography techniques for generating a three-dimensional object. In the appendix of this patent, multiple irradiation passes are used for forming laminae. There is no mention anywhere in this reference the purpose of the multiple passes nor does there appear to be an intentional delay between irradiation passes. This reference fails to teach the utility of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of vectors, let alone teaching the use of a clock to count down a delay time.
European Patent 0 250 121 B1 issued Nov. 2, 1994, to Pomerantz et al. discloses a Stereolithography technique for controlling spatial distortion due to shrinkage of the solidifiable material upon solidification. This technique teaches that radiation of the liquid layer is carried out such that as shrinkage occurs, additional solidifiable liquid tends to move into the region vacated by the shrinkage and is solidified. This patent also discloses a Stereolithography technique for reducing the effects of shrinkage. This technique teaches that radiation of the liquid layer may be applied through masks in a two or more step checkerboard pattern to restrict shrinkage at any given time to localized areas, whereby the distortions due to shrinkage following the first step are at least partially compensated during solidification from a subsequent step. This reference fails to teach lack of adhesion on a first pass where adhesion occurs on a subsequent pass. In addition, this reference fails to teach a step of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of overlapping vectors, let alone teaching the use of a device to count down a desired delay time.
U.S. Pat. No. 5,965,079 to Gigl et al. discloses various Stereolithography techniques for increasing structural integrity while reducing the need for post-curing; for obtaining uniform exposure in regions of intersecting vectors of different types; for determining cure depth; and for reducing distortion due to shrinkage, curl, and post cure.
In U.S. Pat. No. 5,965,079, a stereolithography technique named xe2x80x9ctilingxe2x80x9d is described. Tiling is a method of forming a lamina of an object produced by stereolithography, wherein the lamina is divided into a series of area elements or tiles. Each area element is isolated from adjacent area elements by spacings. The spacings around each area element remain untransformed, at least until all neighboring area elements or tiles are transformed or solidified. The spacings between the individual tiles are left untransformed to act as stess relief zones. The width of the spacing is typically small compared to the width of the individual tiles.
U.S. Pat. No. 5,965,079 discloses that it has long been suspected and recently experimentally verified that shrinkage of curing material can still be occurring several seconds after exposure of an area is suspended. The application states that, as the building material is cured, using preferred materials (XB 5081), there is a delay of approximately 2-3 seconds prior to shrinkage of the material. Thus, the application suggests that the grouping between the tiles is cured after the tiles have been allowed to shrink (e.g., generally at least a 3-second delay between completing neighboring tiles and beginning to grout). In addition, it teaches that the tiles can be partially cured (e.g., a one line trace) followed by partial curing of other tiles, and then returning one or more times to fully cure the previously partially cured tiles.
Another embodiment of U.S. Pat. No. 5,965,079 forms a lamina on which the gaps will be closed by floating at least one end of the solidified material which spans the gap until after at least a substantial portion of the shrinkage has occurred. After allowing for shrinkage to occur, the floating end(s) can be tacked down with rivets, or multipass, or the like.
It is also taught in U.S. Pat. No. 5,965,079 that long vectors can cause tremendous amounts of curl if they are cured and adhered to a previous layer while they are still shrinking. In the case of a floating vector, it may occur where the ends of the vector attach to a boundary. A distortion reduction technique called xe2x80x9cACESxe2x80x9d is described. Using ACES, the first set of skin vectors exposed is given an exposure that results in a net cure depth of slightly under one layer thickness. When the second set of vectors expose the material, the increase in cure depth results in adhesion. When using epoxy resins like SL 5170 and SL 5180, it has been found helpful to allow a time period of between 5 and 90 seconds after exposure of each cross-section before beginning the recoating process so as to allow the modulus of the exposed resin to increase to a certain minimum level before subjecting the newly exposed layer to the forces involved in recoating. This time period is called xe2x80x9cpredip delayxe2x80x9d. As a technique for eliminating or at least minimizing the impact that predip delay has on part building time, it is possible to use a smart exposure pattern that exposes critical areas first, followed by exposure of less critical areas. In effect, the count down of the predip delay time can begin as soon as all critical regions have been exposed.
Another distortion reduction technique disclosed is called xe2x80x9clog jamxe2x80x9d. xe2x80x9cLog Jamxe2x80x9d refers to a scanning technique where some internal hatch (or fill) vectors are retracted from the layer borders to avoid adhesion, wherein after exposure of the hatch or fill an offset border or the like is scanned to attach the hatch and original border.
This reference fails to teach the utility of ensuring enough time has passed after exposure of a first set of vectors for the shrinkage rate to decline to an acceptable level, prior to exposure of a second set of perpendicularly overlapping vectors, let alone teaching the use of a clock to count down a delay time between exposures of perpendicularly overlapping vectors on one layer.
All publications, applications and patents referred to in this section are hereby incorporated by reference as if set forth in full.
A need exists in the art for simplified techniques that can be used to rapidly form objects with less distortion than previously possible, and more particularly, with less distortion than was reliably allowed when using high scan rates for solidifying the material.
2. Other Related Patents, Applications and Publications
The patents, applications and publications in the following Table 1 are hereby incorporated by reference as if set forth in full. Table 1 provides a table of patents and applications co-owned by the assignee of the instant application. A brief description of subject matter found in each patent, application and publication is included in the table to aid the reader in finding specific types of teachings. It is not intended that the incorporation of subject matter be limited to those topics specifically indicated, but instead the incorporation is to include all subject matter found in these publications, applications and patents. The teachings in these incorporated references can be combined with the teachings of the instant application in many ways. For example, the references directed to various data manipulation techniques may be combined with the teachings herein to derive even more useful, modified object data that can be used to more accurately and/or efficiently form objects. As another example, the various apparatus configurations disclosed in these references may be used in conjunction with the novel features of the instant invention.
The following two books are also incorporated by reference herein as if set forth in full: (1) Rapid Prototyping and Manufacturing: Fundamentals of Stereolithograyhy, by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1992; and (2) Stereolithography and other RPandM Technologies: from Rapid Prototyping to Rapid Tooling; by Paul F. Jacobs; published by the Society of Manufacturing Engineers, Dearborn Mich.; 1996.
A first aspect of the invention is to provide a method of forming at least a portion of a three-dimensional object, including: a) forming a layer of fluid-like material over a previously formed lamina of the object, b) exposing the layer to stimulation to form a subsequent lamina of the object adhered to the previously formed lamina, c) repeating (a) and (b) to form the object from a plurality of adhered laminae, and d) defining a time period. Exposing the layer includes exposing at least one element of one layer with at least two exposures. A first exposure is followed by a second exposure after lapse substantially equal to or greater than the defined time period. The first exposure is performed by a beam scanning in a first direction over the element and the second exposure is performed by the beam scanning in a second direction over the element. The first and second directions are different.
A second aspect of the invention is to provide a method of forming at least a portion of a three-dimensional object including: a) forming a layer of fluid-like material over a previously formed lamina of the object, b) exposing the layer to stimulation to form a subsequent lamina of the object adhered to the previously formed lamina, c) repeating (a) and (b) to form the object from a plurality of adhered laminae, and d) defining a time period (DTP). At least one lamina to be formed includes at least first and second isolated regions. Exposing the layer includes exposing the layer with at least first and second exposures. A first exposure of the first region is completed at a time CT11 and the first exposure of the second region is completed at a time CT21 and a second exposure of the first region begins at a time BT12 and the second exposure of the second region begins at a time BT22 fulfilling the equations, DTPxcx9cxe2x89xa6BT12xe2x88x92CT11, and DTPxcx9cxe2x89xa6BT22xe2x88x92CT21, where CT11, CT21, BT12, and BT22 follow after one another respectively.
A third aspect of the invention is to provide a method for forming at least a portion of a three-dimensional object including: a) forming a layer of fluid-like material over a previously formed lamina of the object, b) exposing the layer to stimulation to form a subsequent lamina of the object adhered to the previously formed lamina, c) repeating (a) and (b) to form the object from a plurality of adhered laminae, and d) defining a time period. Exposing the layer includes exposing at least one element of one layer with at least two exposures. A first exposure is completed at a time T1 and a second exposure begins at a time T2 and the difference between T1 and T2 is substantially equal to or greater than the defined time period.
A fourth aspect of the invention is to provide a method for forming at least a portion of a three-dimensional object including: a) forming a layer of fluid-like material over a previously formed lamina of the object, b) exposing the layer to stimulation to form a subsequent lamina of the object adhered to the previously formed lamina, c) repeating (a) and (b) to form the object from a plurality of adhered laminae, and d) defining a time period. At least one lamina to be formed includes at least two regions and exposing the layer includes exposing the layer with at least two exposures. A first exposure exposes a first region and at least a second region, and the at least second exposure exposes a first region and at least second region. The time between the completion of the first exposure of at least one of the exposed regions and the beginning of the second exposure of the exposed region is substantially equal to or greater than the defined time period.
A fifth aspect of the invention is to provide a method for forming at least a portion of a three-dimensional object, including: a) forming a layer of fluid-like material over a previously formed lamina of the object, b) exposing the layer to stimulation to form a subsequent lamina of the object adhered to the previously formed lamina, c) repeating (a) and (b) to form the object from a plurality of adhered laminae, and d) defining a time period. Exposing the layer includes exposing at least one point of one layer with at least two exposures. A first exposure is followed by a second exposure after lapse of the defined tire period. The first exposure is performed by a beam scanning in a first direction over the element. The second exposure is performed by a beam scanning in a second direction over the element. The first and second directions are different, and at least one point receives a first exposure at a time T1, and a second exposure at a time T2 according to the equation T2xe2x88x92T1xcx9cxe2x89xa7DTP, wherein T1 and T2 follow one another consecutively.
A sixth aspect of the invention is to provide an apparatus for forming at least a portion of a three-dimensional object, including a) a coating system for forming a layer of fluid-like material over a previously formed lamina of the object, b) an exposure system for forming a subsequent lamina of the object adhered to the previously formed lamina, c) a computer programmed to operate (a) and (b) to form the object from a plurality of adhered laminae, and d) a computer programmed to utilize a defined time period. The exposure system is operated to form at least one element of one layer with at least two exposures. A first exposure is completed at a time T1 and a second exposure begins at a time T2 and the difference between T1 and T2 is substantially equal to or greater than the defined time period.
A seventh aspect of the invention is to provide an apparatus for forming at least a portion of a three-dimensional object, including a) means for forming a layer of fluid-like material over a previously formed lamina of the object, b) means for forming a subsequent lamina of the object adhered to the previously formed lamina, c) means for operating (a) and (b) to form the object from a plurality of adhered laminae, and d) means for defining a time period. The means for forming a subsequent lamina is operated to form at least one element of one layer with at least two exposures. A first exposure is completed at a time T1 and a second exposure begins at a time T2 and the difference between T1 and T2 is substantially equal to or greater then the defined time period. Other aspects of the invention supply apparatus for implementing the method aspects of the invention noted above.
Additional aspects of the invention will be clear from the embodiments of the invention described below, in conjunction with the Figures associated therewith. Further aspects of the invention involve those referenced above as well as other aspects, to be practiced alone and in various combinations with one another.